Emotion shapes society.
It's a circular process. Some emotional event shapes a person's worldview. They rationalize their emotions into morals and values. Then they go out and try to shape the moral and values of others by appealing to their emotions. Sometimes they rely on logic, sometimes they rely on emotions themselves.
Culture is as flexible as the moral and values that underlie society itself. If a society is driven by the emotion of fear then their culture will reflect it. If it is a society driven by optimism then they will have a culture that reflects that. As the emotional state of a society changes so will the culture.
Insisting that cultures are permanent and unchanging is like insisting that people never change their emotional state. That we're always happy, sad, angry, whatever without change. But that's not true.
An interesting long running study suggests that our personalities at 77 are completely different than our personalities at 14. If (emphasis on if) we're completely different people later in life than we are in our youth, it stands to reason that our morals and values that underlie our culture will change as well. And that means that our culture is probably fluctuating in response to so many factors that we probably shouldn't even argue that any modern culture is identical to that of even 100 years ago.
http://www.sciencealert.com/you-re-...4-and-77-years-old-personality-study-suggests